European Nuclear Medicine Guide
It is a substitute for the reference, cold, product, para-aminohippuric acid (PAH).
It can be labelled also with iodine-131 or iodine-125.
Orthoiodohippurate is a small molecule (327 g.mol-1) and binds, reversibly, to plasma proteins (60-70%). It is partly (15%) filtered in the glomeruli, but the major portion (65%) is secreted in the proximal part of tubules by the organic anion transporters. This leads to a very high first-pass extraction rate of circa 80%, which is much higher than that of [99mTc]Tc-DTPA and significantly better than that of other agents.
It has minimal hepatobiliary elimination (<0.4%).
[123I]OIH, even more than other tubular agents ([99mTc]Tc-MAG3 and [99mTc]Tc-bisicate), has a high extraction rate, thereby leading to high image quality. In most cases, the tubular and glomerular functions are parallel, so the split renal function can be assessed with OIH as well as with [99mTc]Tc-DTPA. Exceptions are:
In either case, [123I]OIH secretion can be preserved, even when glomerular filtration is severely decreased.
When renal function is low, the high extraction makes [123I]OIH even more efficient than [99mTc]Tc-DTPA to assess split function.
The suggested activities to administer are
In paediatric nuclear medicine, the activities should be modified according to the EANM paediatric dosage card (https://www.eanm.org/publications/dosage-calculator/). The minimum recommended activity to administer is 10 MBq.
The effective dose for [123I]OIH is 12 µSv/MBq [109]. The organ with the highest absorbed dose is the urinary bladder: 190 µGy/MBq. By letting the patient empty their bladder 1 h after administration the effective dose lowers to 4.6 µSv/MBq.
The effective dose for [123I]OIH is: 0.90 mSv per procedure.
Caveat:
“Effective Dose” is a protection quantity that provides a dose value related to the probability of health detriment to an adult reference person due to stochastic effects from exposure to low doses of ionizing radiation. It should not be used to quantify the radiation risk for a single individual associated with a particular nuclear medicine examination. It is used to characterize a certain examination in comparison to alternatives, but it should be emphasized that if the actual risk to a certain patient population is to be assessed, it is mandatory to apply risk factors (per mSv) that are appropriate for the gender, the age distribution and the disease state of that population."
After basic, visual assessment, the relative renal function should be measured by tracing renal ROIs and background ROIs (ideally perirenal rings) to get a corrected renogram. The best quantifying method is the Rutland-Patlak graph, which requires placing the heart into the field of view. Alternatively, the area method (taken between 1- and 2-min post-injection, and in any case well before the peak activity has been reached) can be used.
In patients with low renal function, the liver activity must be considered when assessing the right kidney function.
Care should be taken to ensure the patient is adequately hydrated before scanning
If a diuresis renography is considered, prior hydration should be ensured, per os if possible, with circa 7 mL/kg body weight. When i.v. infusion must be used, a sodium-low solute must be used to ensure a rapid diuresis, such as 5% glucose solution. In infants, however, a pure glucose solution is dangerous, and mixed saline-glucose solution is recommended.
Probenecid is taken by the same organic ion transporters with possible competition. Discontinuation should be considered.
There are no EANM procedure guidelines, but information regarding the methodology can be found in the published literature [114,115].